Polyolefin resins such as polypropylene have been widely used as plastics for home appliances and automobile parts because of their low costs and excellent resin properties such as processability, water resistance and oil resistance. To enhance their additional values, a coating layer is formed on the surface of polyolefin molded articles, or polyolefin and another resin are made into laminates. However, since polyolefin has a low polarity, the adhesion of general paints or other resins to polyolefin is poor.
To solve this problem, it has been hitherto attempted to increase the surface polarity of polyolefin molded articles so as to improve the adhesion to paints or other resins by treating the surface in advance with chromic acid, fire flame, corona discharge, plasma, solvent, etc. However, these treatments have problems of needing complicated procedures and being dangerous because of the use of a large amount of corrosive chemicals.
Under these circumstances, there has been proposed a method in which the surface of polyolefin molded articles is coated with a primer mainly made of a chlorinated polyolefin. However, since the chlorinated polyolefin should be dissolved in an aromatic organic solvent harmful to human body, such as toluene and xylene, the method causes safety and environmental problems. To solve the problems, there has been proposed a method to make the chlorinated polyolefin water-dispersible (JP 1-256556A and JP 4-218548A). However, this method also fails to completely eliminate the use of the aromatic organic solvents, and the obtained coating film is poor in weatherability and water resistance. Moreover, it has been demanded to develop an aqueous dispersion adhesive free from chlorine in view of preventing the generation of hydrogen chloride gas upon waste incineration and a good recycling capability.